Variable gear ratio transmission

ABSTRACT

The multi-step automatic transmission with a number of clutches and brakes which at least partly are designed as wet-running, multi-disk clutches wherein with each clutch is associated a hydraulic piston ( 1 ), is provided with a baffle plate ( 2 ) for the fluid within or outside the clutch for adapting the shifting forces to low torques so that an additional pressure chamber ( 3 ) is formed which does not impair the total stroke of the piston ( 1 ).

FIELD OF THE INVENTION

This invention relates to a multi-step automatic transmission for motorvehicles having a plurality of clutches and brakes designed at leastpartly as wet-running, multi-disk clutches with inner and outer diskcarriers each provided with one set of disks.

BACKGROUND OF THE INVENTION

Multi-step automatic transmissions for motor vehicles are widely known.EP-B 434 525 thus describes an automatic transmission for motor vehicleswhich has planetary gear sets shifted by means of clutches and brakesand connected with a hydraulic torque converter provided with a lock-upclutch. The automatic transmission further has an input shaft and anoutput shaft with a double planetary gear set, at least one power pathbetween the input shaft and the double planetary gear set, the same asthree clutches and two brakes, the selective engagement by pairs ofwhich determines different reduction ratios between the input shaft andthe output shaft. Six forward gears and one reverse gear can be obtainedby the three clutches and two brakes.

In motor vehicles having automatic transmissions, there occur in certainsituations such as during positive and negative load change, shiftingjerks that impair the comfort. In order to prevent such a shifting jerkduring the gear shift of the automatic transmission, it was alreadyproposed in DE-C 29 35 916 that the torque of the internal combustionengine be reduced during the gear shift. Together with the reduction ofthe shifting jerk, it is also possible, by virtue of the torque of theinternal combustion engine reduced during the shifting process, toreduce the grinding time of the friction clutches of the automatictransmission that take part in the gear shift so that less wear andslighter heating of the friction elements occur. The control electronicsystem for the internal combustion engine is equipped with anidentification shifting system which, during gear shift, receives fromthe transmission control a shifting signal. In a memory of the controldevice for the internal combustion engine characteristic fields arestored according to which the ignition angle and/or the injection pulsewidth are controlled according to load and rotational speed. The exactdetection of the moment of reduction of the torque is problematic here.

DE-A 40 37 092 describes a method for control of the torque by means ofan internal combustion engine connected with an automatic transmissionwhich is driven by the internal combustion engine, there beingassociated with the latter a control electronic system, which based onrotational speed, load and optionally temperature signals, controls theignition angle of the ignition device and/or the injection pulse widthof the fuel injection device. A transmission electronic systemassociated with the automatic transmission controls for its part, basedon rotational speed and load requirement signals, the gear shifts of theautomatic transmission.

One other possibility of improving the comfort in shifting consists inassociating with the engine electronic system so-called comfort filtersas dampers of load change and jerks, the periods of time of the comfortfilters between the driver's wish and ratio of the inner engine beingpreset exclusively by the electronic system of the internal combustionengine.

Another problem in modern multi-step automatic transmissions consists inthat, on one hand, to maintain very high static torques with one clutchand, on the other, with the same clutch to govern gear shifts withslight load or rolling out gear shifts absolutely without load, createsserious problems. In the design of the clutch, compromises have to bemade here which impair the comfort during shifting.

The problem to be solved by this invention is to configure a multi-stepautomatic transmission for motor vehicles so that the impairments tocomfort in shifting do not occur.

Based on a multi-step automatic transmission of the kind specifiedabove, the problem is solved with the features stated in thecharacteristic part of claim 1; advantageous developments are describedin the sub-claims.

SUMMARY OF THE INVENTION

The invention, therefore, proposes that the piston space of the clutchis divided by a baffle plate for the hydraulic oil so that first andsecond pressure chambers are formed configured so that the total strokeof the piston is not impaired.

The baffle plate can be located inside or outside the clutch; inasmuchas the required differential surface is not obtained by the two pressurechambers separated from each other by the baffle plate, each pressurechamber is advantageously provided with a fluid pipe so that the twopressure chambers can be loaded with different pressures.

Therefore with the inventive development, the advantage obtained is thatby providing a differential surface on the same clutch, the large pistonsurface needed for the high static retaining torque of the clutch isreduced so that the gear shifts can be reduced according to thedifferential surface; this means an optimal adaptation of the clutch tohigh retaining torques and low shifting torques without an additionalclutch that increases the expenses. The differential surface formed hereis easily controlled by the electronic control unit of the transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail with reference to the drawingswhere two advantageous embodiments are shown. In the drawings:

FIG. 1 is a partial section through a multi-step automatic transmissionwith one baffle plate situated within the clutch; and

FIG. 2 is a partial section through a multi-step automatic transmissionwith one baffle plate situated outside the clutch.

DETAILED DESCRIPTION OF THE INVENTION

Since the expert is familiar with multi-step automatic transmissions, inthe enclosed figures, where the same parts are provided with the samereference numeral, only the parts needed for understanding of theinvention are provided with reference numerals.

In the partial section shown in FIG. 1, with 1 is designated thehydraulic piston for actuating a wet-running, multi-disk clutch of amulti-step automatic transmission designated with D on which is frontmounted a baffle plate 2 in a manner such that in the clutch D a firstpressure chamber 3 is formed which is controlled so that the totalstroke of the piston 1 is not hindered. In case of gear shifts with lowtorque requirement, i.e. in gear shifts with small load or in roll outgear shifts without load, both the second pressure chamber 4 and thefirst pressure chamber 3 separated by the baffle plate 2 are suppliedwith equal fluid pressure.

Due to the opposite support of the pressure forces, the difference ofthe two pressure surfaces now becomes only more operative so that theshifting forces are adapted to the low torque to be shifted.

In the embodiment shown in FIG. 1, the baffle plate 2 is situated withinthe clutch D; in the embodiment shown in FIG. 2, the baffle plate 2 issituated outside the clutch, the first pressure chamber formed betweenpiston 1 and piston 2 being here also designated with 3; and the secondpressure chamber formed besides piston 1 being here also designated with4.

Inasmuch as for constructional reasons, it is not possible to obtain theneeded differential surface so that during opposite support of thepressure forces no difference of the two pressure surfaces is operative,the two pressure chambers can also be loaded with different pressures inorder to make the gear shifts sensitive by slight shifting forces; tothis end the two pressure chambers 3, 4 are then each to be providedwith an individual fluid pipe and separately controlled.

Reference Numerals

1 piston

2 baffle plate

3 pressure chamber

4 pressure chamber

5 D clutch

What is claimed is:
 1. A multi-step automatic transmission for a motorvehicle with a plurality of clutches and brakes which are designed, atleast partly, as wet-running multi-disk clutches with inner and outerdisk carriers, and each of the inner disk carriers having a disk set andeach of the outer disk carriers having a disk set, the disk set of theinner disk carrier together with an associated disk set of the outerdisk carrier forming a clutch, and a hydraulic piston (1) beingassociated with each clutch for engaging and disengaging the clutch;wherein a baffle plate (2) is associated with the piston (1) of theclutch such that the piston space is separated into a first pressurechamber (3) and a second pressure chamber (4), and the first pressurechamber (3) and the second pressure chamber (4) are both loadable with adesired variable pressure without hindering a total stroke of the piston(1).
 2. The multi-step automatic transmission according to claim 1,wherein the baffle plate (2) is situated inside the clutch.
 3. Themulti-step automatic transmission according to claim 1, wherein each ofthe first pressure chamber (3) and the second pressure chamber (4) isprovided with a fluid pipe to supply the respective pressure chamberswith different pressures.
 4. The multi-step automatic transmissionaccording to claim 1, wherein the pressure of the first pressure chamber(3) and the pressure of the second pressure chamber (4) areindependently variable.
 5. The multi-step automatic transmissionaccording to claim 1, wherein the pressure of the first pressure chamber(3) and the pressure of the second pressure chamber (4) are modulatedIndependently of one another.
 6. A multi-step automatic transmission fora motor vehicle with a number of clutches and brakes which at leastpartly are designed as wet-running multi-disk clutches with inner andouter disk carriers each provided with a disk set, the disk set of aninner disk carrier together with an associated disk set of the outerdisk carrier forming a clutch and with each clutch is associated ahydraulic piston (1) for engaging and disengaging the clutch, whereinwith the piston (1) of the clutch is associated a baffle plate (2) forthe hydraulic fluid in a manner such that a first pressure chamber (3)and a second pressure chamber (4) are formed which can be loaded with avariable pressure and are designed so as not to hinder the total strokeof the piston (1); and the baffle plate (2) is situated outside theclutch.
 7. A multi-step automatic transmission for a motor vehicle witha plurality of clutches and brakes which are designed, at least partly,as wet-running multi-disk clutches with inner and outer disk carriers,and each of the inner disk carriers having a disk set and each of theouterdisk carriers having a disk set, the disk set of the inner diskcarrier together with an associated disk set of the outer disk carrierforming a clutch, and a hydraulic piston (1) being associated with eachclutch for engaging and disengaging the clutch; wherein a baffle plate(2) is associated with the piston (1) of the clutch such that the pistonspace is divided into a first pressure chamber (3) and a second pressurechamber (4), the first and second pressure chambers are each loadablewith a desired variable pressure without hindering a total stroke of thepiston (1), and the baffle plate (2) is situated outside the clutch.